Stereoscopic video displays can be used to display both 2D and 3D video signals, by processing the frames of the signals depending on the type of signal. The type of the signal can be specified manually by the user, which can be troublesome for inexperienced users. The type of signal can be also specified by supplementary data included in the signal itself or by a supplementary signal, which requires the video display unit to be able to decode and recognize the supplementary data or the supplementary signal.
A US patent application US2009/0009508 presents an apparatus and a method for driving a 2D/3D switchable display, which includes an image mode determination unit determining whether input image signals of continuous frames are in a 2D mode or 3D mode. The 3D mode is recognized by determining a syntax indicating a stereo or a multiview image included in the header information of the input image signal. Alternatively, the image mode can be determined based on the presence of a stereo sync signal. Therefore, the mode determination requires data or signals supplementary to the basic image data.
A PCT patent application WO2010/014973 presents a method and an apparatus for encoding or tagging a video frame which provide a way to indicate, to a receiver, whether the video content is 3-D content or 2-D content, by replacing lines of at least one video frame in a 3-D content with a specific color or pattern. Therefore, the method is useful only for receivers, which are able to recognize the specific color or patterns as an indication of a 3-D content.
A US patent application US2010/182404 presents a 3D video reproduction apparatus, system and method, wherein a input video frame type is detected. The detection is performed by carried out by analyzing difference signals, one difference signal indicating the difference between the left and right side of the image and another difference signal indicating the difference between the top and bottom side of the image. If one of the difference signals is lower than a predetermined value, this indicates a particular type of a 3D frame. If both difference signals are higher than a predetermined value, this indicates a 2D frame. Therefore, the 3D and 2D frame type is determined according to the same type of difference signals.
A US patent application US2009/195774 presents an image analyzed, wherein a parallax is calculated the calculation involves phase correlation analysis between image parts. However, the process is not related to detection whether the frame is of a 3D or 2D type.
In an article “Stereo disparity analysis using phase correlation” by Papadimitriou D V et al (Electronic Letters, IEE Stevenage, GB, vol. 30, no. 18, pp. 1475-1477, ISSN: 0013-5194), a method of image processing by phase correlation is described to increase the speed and accuracy of stereo matching.
In case the display lacks the functionality of decoding supplementary data included in the signal or is not able to decode supplementary signals describing the video type, or the video signal contains only basic image contents without the image type indicated, the signal must be recognized in an alternative way.
The aim of the present invention is to provide a method for determining the video frame type by analyzing video signals having no or unknown indication of video frame type.